OpenRaiser/Intern-Atlas huggingface dataset:
Practical Analysis of Codebook Design and Frequency Offset Estimation for Virtual-MIMO Systems
Venue: arXiv cs.IT 2013
Year: 2013

A virtual multiple-input multiple-output (MIMO) wireless system using the receiver-side cooperation with the compress-and-forward (CF) protocol, is an alternative to a point-to-point MIMO system, when a single receiver is not equipped with multiple antennas. It is evident that the practicality of CF cooperation will be greatly enhanced if an efficient source coding technique can be used at the relay. It is even more desirable that CF cooperation should not be unduly sensitive to carrier frequency offsets (CFOs). This paper presents a practical study of these two issues. Firstly, codebook designs of the Voronoi vector quantization (VQ) and the tree-structure vector quantization (TSVQ) to enable CF cooperation at the relay are described. A comparison in terms of the codebook design and encoding complexity is analyzed. It is shown that the TSVQ is much simpler to design and operate, and can achieve a favorable performance-complexity tradeoff. Furthermore, this paper demonstrates that CFO can lead to significant performance degradation for the virtual MIMO system. To overcome this, it is proposed to maintain clock synchronization and jointly estimate the CFO between the relay and the destination. This approach is shown to provide a significant performance improvement.
On Randomized Sensing and Access Schemes in Wireless Ad-Hoc Cognitive Networks
Venue: arXiv cs.NI 2013
Year: 2013

Over the past decade we have witnessed a rapid growth and development in wireless communication systems, to the point that conventional spectrum allocation policies may not be able to fulfill them all. Federal Communications Commission (FCC) licenses certain frequency segments to a particular user in a particular geographic area. Industrial, Scientific and Medical (ISM) radio bands have also been envisioned for all other unlicensed user to share, as long as they follow certain power regulations. But with the recent boom in the wireless technologies, these open channels have become overcrowded with everything from wireless networks to wireless controllers. Therefore, the regulatory and standardization agencies have been working on new spectrum regulation policies for wireless communication systems. The underlying idea is to let unlicensed users to use the licensed band as long as they can guarantee low interference to the licensed users. Though seemingly simple, sophisticated interference management protocols are needed to meet the expected level of transparency accepted by licensed users. In this report we adopt the dynamic spectrum access approach to limit the interference to primary users and analyze the performance of the cognitive MAC protocols based on randomized sensing and access schemes.
Surveillance Video Processing Using Compressive Sensing
Venue: arXiv cs.CV 2013
Year: 2013

A compressive sensing method combined with decomposition of a matrix formed with image frames of a surveillance video into low rank and sparse matrices is proposed to segment the background and extract moving objects in a surveillance video. The video is acquired by compressive measurements, and the measurements are used to reconstruct the video by a low rank and sparse decomposition of matrix. The low rank component represents the background, and the sparse component is used to identify moving objects in the surveillance video. The decomposition is performed by an augmented Lagrangian alternating direction method. Experiments are carried out to demonstrate that moving objects can be reliably extracted with a small amount of measurements.
Randomized partition trees for exact nearest neighbor search
Venue: arXiv cs.DS 2013
Year: 2013

The k-d tree was one of the first spatial data structures proposed for nearest neighbor search. Its efficacy is diminished in high-dimensional spaces, but several variants, with randomization and overlapping cells, have proved to be successful in practice. We analyze three such schemes. We show that the probability that they fail to find the nearest neighbor, for any data set and any query point, is directly related to a simple potential function that captures the difficulty of the point configuration. We then bound this potential function in two situations of interest: the first, when data come from a doubling measure, and the second, when the data are documents from a topic model.
Persistence modules: Algebra and algorithms
Venue: arXiv cs.CG 2013
Year: 2013

Persistent homology was shown by Carlsson and Zomorodian to be homology of graded chain complexes with coefficients in the graded ring $\kk[t]$. As such, the behavior of persistence modules -- graded modules over $\kk[t]$ is an important part in the analysis and computation of persistent homology. In this paper we present a number of facts about persistence modules; ranging from the well-known but under-utilized to the reconstruction of techniques to work in a purely algebraic approach to persistent homology. In particular, the results we present give concrete algorithms to compute the persistent homology of a simplicial complex with torsion in the chain complex.
Improving success probability and embedding efficiency in code based steganography
Venue: arXiv cs.IT 2013
Year: 2013

For stegoschemes arising from error correcting codes, embedding depends on a decoding map for the corresponding code. As decoding maps are usually not complete, embedding can fail. We propose a method to ensure or increase the probability of embedding success for these stegoschemes. This method is based on puncturing codes. We show how the use of punctured codes may also increase the embedding efficiency of the obtained stegoschemes.
Optimal Throughput-Outage Trade-off in Wireless One-Hop Caching Networks
Venue: arXiv cs.IT 2013
Year: 2013

We consider a wireless device-to-device (D2D) network where the nodes have cached information from a library of possible files. Inspired by the current trend in the standardization of the D2D mode for 4th generation wireless networks, we restrict to one-hop communication: each node place a request to a file in the library, and downloads from some other node which has the requested file in its cache through a direct communication link, without going through a base station. We describe the physical layer communication through a simple "protocol-model", based on interference avoidance (independent set scheduling). For this network we define the outage-throughput tradeoff problem and characterize the optimal scaling laws for various regimes where both the number of nodes and the files in the library grow to infinity.
Representation, simplification and display of fractional powers of rational numbers in computer algebra
Venue: arXiv cs.SC 2013
Year: 2013

Simplification of fractional powers of positive rational numbers and of sums, products and powers of such numbers is taught in beginning algebra. Such numbers can often be expressed in many ways, as this article discusses in some detail. Since they are such a restricted subset of algebraic numbers, it might seem that good simplification of them must already be implemented in all widely used computer algebra systems. However, the algorithm taught in beginning algebra uses integer factorization, which can consume unacceptable time for the large numbers that often arise within computer algebra. Therefore some systems apparently use various ad hoc techniques that can return an incorrect result because of not simplifying to 0 the difference between two equivalent such expressions. Even systems that avoid this flaw often do not return the same result for all equivalent such input forms, or return an unnecessarily bulky result that does not have any other compensating useful property. This article identifies some of these deficiencies, then describes the advantages and disadvantages of various alternative forms and how to overcome the deficiencies without costly integer factorization.
Efficient Data Gathering in Wireless Sensor Networks Based on Matrix Completion and Compressive Sensing
Venue: arXiv cs.NI 2013
Year: 2013

Gathering data in an energy efficient manner in wireless sensor networks is an important design challenge. In wireless sensor networks, the readings of sensors always exhibit intra-temporal and inter-spatial correlations. Therefore, in this letter, we use low rank matrix completion theory to explore the inter-spatial correlation and use compressive sensing theory to take advantage of intra-temporal correlation. Our method, dubbed MCCS, can significantly reduce the amount of data that each sensor must send through network and to the sink, thus prolong the lifetime of the whole networks. Experiments using real datasets demonstrate the feasibility and efficacy of our MCCS method.
On Search Engine Evaluation Metrics
Venue: arXiv cs.IR 2013
Year: 2013

The search engine evaluation research has quite a lot metrics available to it. Only recently, the question of the significance of individual metrics started being raised, as these metrics' correlations to real-world user experiences or performance have generally not been well-studied. The first part of this thesis provides an overview of previous literature on the evaluation of search engine evaluation metrics themselves, as well as critiques of and comments on individual studies and approaches. The second part introduces a meta-evaluation metric, the Preference Identification Ratio (PIR), that quantifies the capacity of an evaluation metric to capture users' preferences. Also, a framework for simultaneously evaluating many metrics while varying their parameters and evaluation standards is introduced. Both PIR and the meta-evaluation framework are tested in a study which shows some interesting preliminary results; in particular, the unquestioning adherence to metrics or their ad hoc parameters seems to be disadvantageous. Instead, evaluation methods should themselves be rigorously evaluated with regard to goals set for a particular study.
Turbo DPSK in Bi-directional Relaying
Venue: arXiv cs.IT 2013
Year: 2013

In this paper, iterative differential phase-shift keying (DPSK) demodulation and channel decoding scheme is investigated for the Joint Channel decoding and physical layer Network Coding (JCNC) approach in two-way relaying systems. The Bahl, Cocke, Jelinek, and Raviv (BCJR) algorithm for both coherent and noncoherent detection is derived for soft-in soft-out decoding of DPSK signalling over the two-user multiple-access channel with Rayleigh fading. Then, we propose a pragmatic approach with the JCNC scheme for iteratively exploiting the extrinsic information of the outer code. With coherent detection, we show that DPSK can be well concatenated with simple convolutional codes to achieve excellent coding gain just like in traditional point-to-point communication scenarios. The proposed noncoherent detection, which essentially requires that the channel keeps constant over two consecutive symbols, can work without explicit channel estimation. Simulation results show that the iterative processing converges very fast and most of the coding gain is obtained within two iterations.
VM-MAD: a cloud/cluster software for service-oriented academic environments
Venue: arXiv cs.DC 2013
Year: 2013

The availability of powerful computing hardware in IaaS clouds makes cloud computing attractive also for computational workloads that were up to now almost exclusively run on HPC clusters. In this paper we present the VM-MAD Orchestrator software: an open source framework for cloudbursting Linux-based HPC clusters into IaaS clouds but also computational grids. The Orchestrator is completely modular, allowing flexible configurations of cloudbursting policies. It can be used with any batch system or cloud infrastructure, dynamically extending the cluster when needed. A distinctive feature of our framework is that the policies can be tested and tuned in a simulation mode based on historical or synthetic cluster accounting data. In the paper we also describe how the VM-MAD Orchestrator was used in a production environment at the FGCZ to speed up the analysis of mass spectrometry-based protein data by cloudbursting to the Amazon EC2. The advantages of this hybrid system are shown with a large evaluation run using about hundred large EC2 nodes.
Reasoning About Higher-Order Relational Specifications
Venue: arXiv cs.LO 2013
Year: 2013

The logic of hereditary Harrop formulas (HH) has proven useful for specifying a wide range of formal systems. This logic includes a form of hypothetical judgment that leads to dynamically changing sets of assumptions and that is key to encoding side conditions and contexts that occur frequently in structural operational semantics (SOS) style presentations. Specifications are often useful in reasoning about the systems they describe. The Abella theorem prover supports such reasoning by explicitly embedding the specification logic within a rich reasoning logic; specifications are then reasoned about through this embedding. However, realizing an induction principle in the face of dynamically changing assumption sets is nontrivial and the original Abella system uses only a subset of the HH specification logic for this reason. We develop a method here for supporting inductive reasoning over all of HH. Our approach takes advantage of a focusing property of HH to isolate the use of an assumption and the ability to finitely characterize the structure of any such assumption in the reasoning logic. We demonstrate the effectiveness of these ideas via several specification and meta-theoretic reasoning examples that have been implemented in an extended version of Abella.
Lock-free Concurrent Data Structures
Venue: arXiv cs.DC 2013
Year: 2013

Concurrent data structures are the data sharing side of parallel programming. Data structures give the means to the program to store data, but also provide operations to the program to access and manipulate these data. These operations are implemented through algorithms that have to be efficient. In the sequential setting, data structures are crucially important for the performance of the respective computation. In the parallel programming setting, their importance becomes more crucial because of the increased use of data and resource sharing for utilizing parallelism. The first and main goal of this chapter is to provide a sufficient background and intuition to help the interested reader to navigate in the complex research area of lock-free data structures. The second goal is to offer the programmer familiarity to the subject that will allow her to use truly concurrent methods.
Exploration of Recent Advances in the Field of Brain Computer Interfaces
Venue: arXiv cs.HC 2013
Year: 2013

A new approach for implementing number of expressions, emotions and, actions to operate objects through the thoughts of brain using a Non-Invasive Brain Computing Interface (BCI) technique has been proposed. In this paper a survey on brain and its operations are presented. The steps involved in the brain signal processing are discussed. The current systems are able to present few expressions and emotions on a single device. The proposed system provides the extended number of expressions on multiple numbers of objects.
Randomized online computation with high probability guarantees
Venue: arXiv cs.DS 2013
Year: 2013

We study the relationship between the competitive ratio and the tail distribution of randomized online minimization problems. To this end, we define a broad class of online problems that includes some of the well-studied problems like paging, k-server and metrical task systems on finite metrics, and show that for these problems it is possible to obtain, given an algorithm with constant expected competitive ratio, another algorithm that achieves the same solution quality up to an arbitrarily small constant error a with high probability; the "high probability" statement is in terms of the optimal cost. Furthermore, we show that our assumptions are tight in the sense that removing any of them allows for a counterexample to the theorem. In addition, there are examples of other problems not covered by our definition, where similar high probability results can be obtained.
Structural Diversity for Resisting Community Identification in Published Social Networks
Venue: arXiv cs.SI 2013
Year: 2013

As an increasing number of social networking data is published and shared for commercial and research purposes, privacy issues about the individuals in social networks have become serious concerns. Vertex identification, which identifies a particular user from a network based on background knowledge such as vertex degree, is one of the most important problems that has been addressed. In reality, however, each individual in a social network is inclined to be associated with not only a vertex identity but also a community identity, which can represent the personal privacy information sensitive to the public, such as political party affiliation. This paper first addresses the new privacy issue, referred to as community identification, by showing that the community identity of a victim can still be inferred even though the social network is protected by existing anonymity schemes. For this problem, we then propose the concept of \textit{structural diversity} to provide the anonymity of the community identities. The $k$-Structural Diversity Anonymization ($k$-SDA) is to ensure sufficient vertices with the same vertex degree in at least $k$ communities in a social network. We propose an Integer Programming formulation to find optimal solutions to $k$-SDA and also devise scalable heuristics to solve large-scale instances of $k$-SDA from different perspectives. The performance studies on real data sets from various perspectives demonstrate the practical utility of the proposed privacy scheme and our anonymization approaches.
Yet another approach to the Maximum Flow
Venue: arXiv cs.DS 2013
Year: 2013

I introduce a new approach to the maximum flow problem by a simple algorithm with a slightly better runtime. This approach is based on sorting arcs insight of vertices on a residual graph. This new approach leads to an O(mn^0.5) time bound for a network with n vertices and m arcs. Category: Algorithms, Graph Theory and maximum flows
Minimum-Link Paths Revisited
Venue: arXiv cs.CG 2013
Year: 2013

A path or a polygonal domain is C-oriented if the orientations of its edges belong to a set of C given orientations; this is a generalization of the notable rectilinear case (C = 2). We study exact and approximation algorithms for minimum-link C-oriented paths and paths with unrestricted orientations, both in C-oriented and in general domains. Our two main algorithms are as follows: A subquadratic-time algorithm with a non-trivial approximation guarantee for general (unrestricted-orientation) minimum-link paths in general domains. An algorithm to find a minimum-link C-oriented path in a C-oriented domain. Our algorithm is simpler and more time-space efficient than the prior algorithm. We also obtain several related results: - 3SUM-hardness of determining the link distance with unrestricted orientations (even in a rectilinear domain). - An optimal algorithm for finding a minimum-link rectilinear path in a rectilinear domain. The algorithm and its analysis are simpler than the existing ones. - An extension of our methods to find a C-oriented minimum-link path in a general (not necessarily C-oriented) domain. - A more efficient algorithm to compute a 2-approximate C-oriented minimum-link path. - A notion of "robust" paths. We show how minimum-link C-oriented paths approximate the robust paths with unrestricted orientations to within an additive error of 1.
Trend prediction in temporal bipartite networks: the case of Movielens, Netflix, and Digg
Venue: arXiv cs.SI 2013
Year: 2013

Online systems where users purchase or collect items of some kind can be effectively represented by temporal bipartite networks where both nodes and links are added with time. We use this representation to predict which items might become popular in the near future. Various prediction methods are evaluated on three distinct datasets originating from popular online services (Movielens, Netflix, and Digg). We show that the prediction performance can be further enhanced if the user social network is known and centrality of individual users in this network is used to weight their actions.
Adaptive Crowdsourcing Algorithms for the Bandit Survey Problem
Venue: arXiv cs.LG 2013
Year: 2013

Very recently crowdsourcing has become the de facto platform for distributing and collecting human computation for a wide range of tasks and applications such as information retrieval, natural language processing and machine learning. Current crowdsourcing platforms have some limitations in the area of quality control. Most of the effort to ensure good quality has to be done by the experimenter who has to manage the number of workers needed to reach good results. We propose a simple model for adaptive quality control in crowdsourced multiple-choice tasks which we call the \emph{bandit survey problem}. This model is related to, but technically different from the well-known multi-armed bandit problem. We present several algorithms for this problem, and support them with analysis and simulations. Our approach is based in our experience conducting relevance evaluation for a large commercial search engine.
Effective Marking Equivalence Checking in Systems with Dynamic Process Creation
Venue: arXiv cs.LO 2013
Year: 2013

The starting point of this work is a framework allowing to model systems with dynamic process creation, equipped with a procedure to detect symmetric executions (ie., which differ only by the identities of processes). This allows to reduce the state space, potentially to an exponentially smaller size, and, because process identifiers are never reused, this also allows to reduce to finite size some infinite state spaces. However, in this approach, the procedure to detect symmetries does not allow for computationally efficient algorithms, mainly because each newly computed state has to be compared with every already reached state. In this paper, we propose a new approach to detect symmetries in this framework that will solve this problem, thus enabling for efficient algorithms. We formalise a canonical representation of states and identify a sufficient condition on the analysed model that guarantees that every symmetry can be detected. For the models that do not fall into this category, our approach is still correct but does not guarantee a maximal reduction of state space.
Alphabet-Dependent String Searching with Wexponential Search Trees
Venue: arXiv cs.DS 2013
Year: 2013

It is widely assumed that $O(m+\lg σ)$ is the best one can do for finding a pattern of length $m$ in a compacted trie storing strings over an alphabet of size $σ$, if one insists on linear-size data structures and deterministic worst-case running times [Cole et al., ICALP'06]. In this article, we first show that a rather straightforward combination of well-known ideas yields $O(m+\lg\lg σ)$ deterministic worst-case searching time for static tries. Then we move on to dynamic tries, where we achieve a worst-case bound of $O(m+\frac{\lg^{2}\lgσ}{\lg\lg\lgσ})$ per query or update, which should again be compared to the previously known $O(m+\lgσ)$ deterministic worst-case bounds [Cole et al., ICALP'06], and to the alphabet \emph{in}dependent $O(m+\sqrt{\lg n/\lg\lg n})$ deterministic worst-case bounds [Andersson and Thorup, SODA'01], where $n$ is the number of nodes in the trie. The basis of our update procedure is a weighted variant of exponential search trees which, while simple, might be of independent interest. As one particular application, the above bounds (static and dynamic) apply to suffix trees. There, an update corresponds to pre- or appending a letter to the text, and an additional goal is to do the updates quicker than rematching entire suffixes. We show how to do this in $O(\lg\lg n + \frac{\lg^{2}\lgσ}{\lg\lg\lgσ})$ time, which improves the previously known $O(\lg n)$ bound [Amir et al., SPIRE'05].